Machine for forming material



March 27, 1945.

G. D. RECHTON EIAL MACHINE FOR FORMING MATERIAL Filed Sept. 7, 1942 4 Sheets-Sheet l I 'IIIIIIIIIIIIII Mardl 7, 1945- s. D. RECHTON arm. 2,372,516

MACHINE FOR FORMING MATERIAL 4 Sheets-Sheet 2 cs. D. RECHTON ETAL I 2,372,516

MACHINE FOR FORMING MATERIAL March 27, 1945.

' Filed Sept. 7, 1942 4 Sheets-Sheet 3 WW5 9 w g 7 z W 5 2 g ww DWHI 5 wa m 6 M BY 2 A f ATTOZ/VE) March 1945- G. D. RECHTON ETAL ,516

MACHINE FOR FORMING MATERIAL Filed Sept. 7, 1942 4 Sheets-Sheet 4 fQU/Z/flE/U/l/ 1 /194515 D/AGBAM D g R g as Q Q Q \E Q 1 Q 012852711 W420 J46? H 144475 00 IN V EN TOR$ Patented Mar. 27, 1945 UNITED STATES PATENT OFFICE MACHINE FOR FORMING MATERIAL Application September 7, 1942, Serial No. 457,630

27 Claims.

This invention relates to a machine for forming bodies of metal and other materials and particularly to a machine for dimpling or otherwise fiexurally forming sheet metal. It also relates to a machine for forming sheets of magnesium alloy and other metals and materials having qualities which prevent theipmeing formed at ordinary temperatures without the development of structural weakness, and particularly to a machine for dimpling, at suitably elevated temperatures, magnesium sheet metal parts for the reception of flush rivets in the manufacture of aircraft, aircraft accessories, or other products.

The word forming, as herein used, means any processing operation which establishes or changes the shape or dimensionsof an article or divides the article into a plurality of articles, such as bending, punching, blanking, stamping and shearing; The invention as to some of its features, is applicable to machines for forming plastic and other non-metallic articles.

The aviation industry, in line with the trend toward lighter and faster aircraft, has been steadily increasing the use of the lighter materials, such as magnesium. Although m'agnesium ranks in eighth place in abundance among the elements of the earths crust, it has not been used extensively in industry until the last few years. The slow adoption of this metal for airplane and other construction has been due in a great degree to difiiculties in perfecting economical and practical methods of processing the same.

There have been many attempts to cold-form sheets of those magnesium alloys characterized by structural strength, which have usually failed of their purpose. For example, in dimpling sheets of magnesium alloys it has been found that incipient fracture cracks will appear adjajacent the sharp radius bend formed at the base of the dimple. .These cracks indicate structural weakness which makes the sheet undesirable for use in aircraft construction.

Research and experimental work has shown that by heating the sheets of magnesium alloys to an ascertained temperature, for example in the case of one alloy to approximately 700 Fahrenheit, these metals can be dimpled or otherwise worked without causing fracture. Follow ing out this discovery, several different methods have been employed to heat the sheet metal preparatory to dimpling, each of which has for one reason or another proven unsatisfactory. One of the methods consists of heating the sheet electrically by passing a current therethrough, using the dimpling dies as electrodes.

in a manner similar to that followed in a spotwelding machine. This method causes the dimpled metal and the dies to become pitted from excessive arcing which takes place due to the insulating qualities of the surface-protecting pickling coat on the magnesium sheet. This difficulty, coupled with excessive heating and consequent softening and deformation of the dies renders a machine for this method of heating metal sheets impractical, and expensive in operation. In order to avoid these undesirable results this invention contemplates the provision of a machine having a heating means which does not involve excessive heating of the dies and does not involve transmitting currents of electricity through the dies or other electrodes and/or the sheet.

This invention is herein shown embodied in an automatic magnesium sheet dimpling device which heats the sheet and dimples it while in heated condition. Two silver faced electric heating elements or heating bodies are provided on the machine which are placed one above the sheet and one below. These elements when heated arebrought into contact with the upper and lower faces of the sheet, securing an even distribution of heat through the sheet adjacent the rivet hole to be dimpled. The dimpling gun is pneumatically operated in accordance with standard practice and the movement of the heating elements into and out of contact with the magnesium sheet is preferably also accomplished by pneumatic means, the selector valves of the pneumatic devices being electrically actuated and their actuation accomplished in a work cycle by a system of electrical relays and other control equipment, the cycle being initiated by a single manually operated switch.

One object of this invention is to provide a dimpling or other forming machine having pneumatically operated dies, in which the pneumatic valves therefor are electrically actuated by a lever under the manual control of the operator.

Another object of the invention is to provide a dimpling or other forming machine which is simple in construction, economical to operate, and completes the cycle of steps of the dimpling operation within a minimum time interval.

Another object of this invention is to rovide a machine for dimpling or otherwise orming sheets of magnesium or other metals or-materials which develop structural weakness when cold formed or which for other reasons should be formed at a high temperature in which the cycle of operativesteps including heating of the metal sheet is initiated by a single act of the operator and is automatic thereafter, excepting the last step which is manually controlled.

Another object of this invention is to provide a machine of the character described havin means for affording a visible indication of its several functions;

Another object of this invention is to provide a machine which,'at the will of the operator, may be utilized to dimple or otherwise form either Dural sheets or sheets of magnesium alloy or other metals or materials which are formed to advantage at relatively high temperatures.

Another object of this invention is to provide a machine of the character described having one of the heating elements is formed to provide aclearance for previously formed dimples, or other raised areas on the sheet.

Another object of this invention is the provision of a machine of the character described in which the heating elements are faced with a metal providing the maximum rate of heat transfer from the heat generating means within the heater to the sheet.

Further objects and advantages of this invention will'be brought out in the following description taken in connection with the accompanyi'ng drawings and appended claims. In the drawin s, which are for illustrative purposes only:

Figure 1 is a side elevation of a dimpling machine embodying this invention.

Figure 2 is a front elevation of the machine shown in Figure 1.

Figure 3 is a schematic view showing the dimpli'ngdevices, the pneumatic mechanism for their operation, and a wiring diagram of the electrical equipment for the heating elements, for control of the pneumatic equipment and for performing other functions in the operation of the machine.

Figure 4 is a fragmentary schematic view showing a modified circuit for supplying current to the heating elements.

Figure 5 is an enlarged sectional View of the dimpling dies and heating elements showing the heating elements in their heating position.

Figure 6 is an enlarged sectional view similar to Figure 5 showing the heating elements in retracted position and the dimpling dies in forming position.

Figure '7 is a plan view of one of the heating elements showing the feature of its construction providing for clearing previously dimpled holes.

Figure 8 is a side elevational view of the heating element shown in Figure '7.

Figure 9 is a side elevation of a modified form of heating element designed to concentrate the heat on a limited area of the sheet adj'acently' surrounding the rivet hole.

Figure 10 is a graph representing the magnesium end of a magnesium aluminum equilibrium phase. diagram.

While a dimpling machine has been selected to disclose this invention, it will be understood that, as to some of its features, the invention is not restricted to a dimpling machine but is applicable to other forming machines.

Figures 1 and 2 show a dimpling machine It having a base 12 upon which is mounted a supporting column I4. A pair of generally horizontal laterally extending arms 16 and 18 are clamped to the column M, the upper arm 18 supporting at its outer end a dimpling gun as sembly 20 and the lower arm l6 supporting at its outer end a lower dimpling anvil assembly 22.

The dimpling gun assembly 20 is slidable vertically reciprocated in the guide l9'at the outer end of the upper arm I8 by a lever 26 which is fulcrumed at 21 between ears 24 extending upwardly from the upper arm I B and which is connected at its outer end to the upper end of the dimpling gun assembly at 34 and is connected at its inner end at 30 to a piston rod 29 of a piston 32 (not shown in Figures 1 and 2) which reciprocates' within a pneumatic cylinder 28. mounted upon the rear end of the upper arm 18; The lever 26 is spring loaded by a spring 42 which. is seated under a compression between a stationary lug and a collar nut 44 on a bolt 38 which passes through an eye 39' in the lug 40 and is pivoted at its outer end to the free end ofa depending arm 36. on the lever 26.. A stop bar 31' is mounted on the'arm l8 to engagev the under side of the rear end of the lever 26 to preventthe piston of the piston rod 29 from striking the bottom of the cylinder 28.

The lower end of the dimpling gun assembly 2ft, including the female die 59 thereof, is. sur-' rounded by a heating element or heating body 52 having an aperture '58. The heating element 52 is held. in position laterally with respect to the dimpling gun assembly and supported vertically by a. iston which is vertically reciprocably movable within a pneumatic cylinder 48 mounted upon the outer end of the upper arm 18 adjacent the inner side of the dimpling gun assembly; Admission. of air to the pneumatic cylinder 48 moves the heating element downwardly and upon exhaust of air from this cylinder, the heating element is retracted to its normal position by the action of a tension spring 56 secured at its upper and lower ends to the guide 19 and piston 50 respectively. A cable 56 contains the electrical conductors for heating the element 52 and registering its temperature.

To the upper face of the outer end of the arm Hi is secured a pneumatic cylinder 60 to which air is supplied at an inlet 62 in which reciprocates a tubular piston 64 (see Figure 5), the piston 64 carrying at its upper end a heating element or heating body 66 which is apertured for the accommodation of a stationary male dimpling die 10. The support for the die 10 extends downwardly through the hollow piston 64 and is mounted upon the lower arm IS. The heating element 66 is thus vertically slidable withrespect tothe stationary dimpl'ing die 10 from a lower retracted position to an upper position in which it makescontact with the metal sheet to be dimpled. A cable 68 contains the conductor wires for supplying the energy to heat the heating element 66 and to register its temperature. A micro switch [2, closed by depression of a button 14 upondownward movement of the heater 66 to its lower retracted position, is connected to the control mechanism by the conductors within a cable 13,. the cables Stand 13 entering a junction box 15 from which electrical connections are made to the control and indicating devices by the conductors in a cable 11.

Y The system of air conduits and pneumatic control devices for operation of the pneumatic cylinders 28, 48 and 60, and for operation of the dimpling gun 20, are shown schematically in Figure 3, some of the conduits and control devices appearing in the structural views, Figures 1 and 2. Air

. enters the machine under pressure at I through a gate valve I02 and may proceed to an electrically controlled valve I04 through the pipe I03 and thence, when valve I04 is opened, through a pipe I32 not seen in Figures 1 and 2 but shown in Figure 3 to cylinder 28 to depress the dimpling un assembly 20.

Air may also pass from the gate valve I02 to the electrically'controlled valve I06 through pipe I05, for transmission when valve I06 is in open position through pipes H8 and I22 to cylinders 48 and 60 for movement'of the heating elements 52 and 66 respectively from their retracted position as shown in Figure 1 to their position of contact with the metal sheet to be dimpled as shown in Figure 5. Electrically controlled exhaust valves H0 and H2 are in closed position when valves I04 and I06 respectively are in open position, and vice versa. They function to relieve the air pressure in cylinder 28 and in cylinders 48 and 60 respectively for the elevation of the dimpling gun in the case of cylinder 28 and the retraction of the heating elements 52 and 68 in the case of the cylinders 48 and 60.

A valve I2I in the pipe I I8 and a pressure gage I23 provide means for regulating the air pressure transmitted to cylinders 48 and 80 at any desired value, thus regulating the degree of pressure at which the heating elements engage the metal sheet. The'section of exhaust pipe in which exhaust valve H0 is placed, the air supply pipe I03 and the pipe I32 leading to the cylinder 28 are connected as shown by a T I30. The exhaust pipe in which valve H2 is placed, the air supply pipe I05 and the pipe II8 leading to the cylinders 48 and 60 are connected as shown by means of a T II6 while pipe H8 is connected to pipe I22-by the T II1.

To T I36 interposed in the air supply pipe I03 is connected a pipe I38 leading to a pressure regulating valve I40, which in conjunction with a pressure gage I42 serves to regulate the air pressure in pipe I44 leading to the dimpling gun assembly 20 and tripping the pneumatic firing device for applying an impulse force to the dimpling die of the dimpling gun assembly when the pressure between the upper and lower dimpling dies reaches a prescribed value after the dimpling gun assembly has been lowered and the two dies brought into engagement with the metal sheet to be dimpled, through depression of the gun due to actuation of the piston 32 operating in cylinder 28.

Upon an angle support 16 secured to the upper arm I8 is mounted a control box 18 which houses the electrical control equipment for the supply of current to the heaters 52 and 66 for sequential control of the electrical devices for the actuation of valves I04, IIO, I06, and H2. These devices and their connections are enclosed within dash lines on Figure 3 and designated by the numeral 18. The valves I04, IIO, I06 and H2 are electrically actuated by solenoids in a manner to be hereinafter explained, the conductors from the control box 18 to the various valve operating solenoids passing through a connection box I08 mounted on the inner end of the upper arm I8.

The front face of the control box 18 serves as a control panel 19 upon which are mounted the several dial switches and other manual controls, and the value registering instruments for use in operating the machine. These several control devices and registering instruments will be referred to and described in the course of the following explanation of the wiring diagram of Figure 3. On this diagram the arrows indicate the direction of potential drop.

Electrical energy is supplied to the control box by a leaddn cable comprising conductors I46 and I41. A warning light 82, connected across these main conductors I46 and I41, is placed on the panel to indicate passage of current to the control devices of the control box and thence to the heating elements and electrically operated air valves. A line switch 83 controls the supply of current to the machine. Conductors I52 and I54 constitute a shunt heating circuit connected to 'the wires I46 and I41 of the power circuit, and

supply electrical energy through a transformer I50 to the heating elements 52 and 66 in parallel through wires I62 and I84. The transformer I58 .is of the variable tap type and includes an adjusting knob 88 for controlling the wattage input and temperature of the heaters. The primary of the transformer I58 is connected to the conductors I52 and I54 by a normally open switch I56. This switch is automatically closed upon closing of the main switch 83 by a relay coil I49 which is connected between power lines I46 and I41 by conductor I5I and conductor I54.

The pressure valve I06 and exhaust valve II2 are operated by solenoids I94 and I96 respectively, each valve being spring retracted to closed position upon the de-energization of the associated solenoid. Solenoid I94 is connectedto power line I41 by a shunt circuit comprising the conductors I1I, I13, switch 209, conductors I15 and I61, and to line I46 by a conductor I69. Exhaust solenoid I96 is connected to the power line I46 by a conductor I69 and to line I41 by a shunt circuit comprising conductors I11, 209, and conductors I15 and I61.

The pressure valve I04 and the discharge valve IIO for operation of the piston 82 in cylinder 28 are actuated by solenoids I and I92 respectively, each valve being spring retracted to its closed position. Inlet solenoid I90 is connected to the power line I46 by the conductor BI and to power line I41 by a shunt circuit comprising the conductor I83 including the micro switch 12, conductor I05, switch I92, conductor I81, selector switch I98 and conductor I61. Solenoid I92 is connected to the power line I46 by the conductor IBI and to line I41 by a shunt circuit comprising conductors I89, I9I, switch 2I1, conductor I81, selector switch I98 and conductor I61.

A control circuit which is connected to the power lines I46 and I41 comprises the conductor I65, the switch 96 operated by the foot pedal 98, as best seen in Figures 1 and 2. and conductor I61 in which is disposed relay coil I 86.

Another control circuit which is also closed by the foot pedal switch 96 and is arranged in parallel with the control relay circuit of the relay I86 comprises conductors I65, I61 and I93, anode I12, and cathode I91 of a rectifier tube I10, conductor I95, conductor 202 in which is disposed relay coil I88, anode I80 and cathode I82 of a gas trig er tube I84, conductors MI and I61. The filament I14 of the rectifier tube I10 is connected I 1 9, switch to the power lines hand I41'by conductors I53, I5I, and I 61. The efiect of the rectifier tube is to impress a direct current potential upon the control relay coil #88 and the anode of the trigger tube I 84.

Current flow from anode I80 to cathode I82 of the gas trigger tube I84 occurs upon charging of the grid 20I to a predetermined value, the resistor 20V limiting current flow from the grid 201 to cathode I82. The grid is charged with a potential voltage to the prescribed value by an RC voltage accumulator circuit I 99 connected between the cathode I91 of the rectifier tube I and the conductor I61. This circuit includes a filtering circuit 209 for filtering the same and the relay circuit. As usual this accumulator circuit comprises resistance and condenser elements as shown, the time interval required for voltage build-up being regulated by the variable resistor I16.

Discharge of the RC circuit is provided for by a discharge circuit comprising the conductor 203 in which is interposed the usual resistance element 205.

When the switch 96 is closed the relay I06 is energized which operates the gauge switch I45 to move switch arm 209 into engagement with contact 201, connecting conductors I13 and I to complete the circuit by which a solenoid I94 is energized 'for the operation of the valve I06.

The'movement of switch arm 209 out of engagement with the contact 2I3 also opens the discharge circuit, and the accumulator circuit begins to charge. When the accumulator circuit is charged with the predetermined voltage the grid actuates the trigger tube I84, allowing current to flow from the anode I80 to cathode I82 and. the relay coil I88 is energized.

Energization of the relay I08 opens the switch 22 in the conductor I61 de-energizing relay coil I8o. De-energization of the relay coil I86 causes the switch arm 209 to be moved into engagement with the contact 2| I to electrically connect conductor I19 with I15 to complete the circuit for energization of solenoid I96 for the operation of the exhaust valve II2. Energization of the relay coil I88 also causes switch arm 2I1 to engage the contact ZIE to electrically connect conductor I05 with the conductor I81 and thus energizethe solenoid 590 which opens the pressure valve I04 for the lowering of the dimpling assembly 20. When the switch 96 is opened the relay I88 is tile-energized and the switch 22I is closed. The de-energization of the relay I88 also causes the switch arm 2I1 to be moved into engagement with contact 2I9 to connect conductor I9I with conductor I81 and completes the circuit for energization of the solenoid I92 for opening the discharge valve IIIl resulting in the elevation. of the dimpling gun assembly 20.

The micro switch 12 is in closed position when the heater element 56 is in its lower-most position and opens at the initiation of the upward movement of this heater in response to opening of the valve H0. The micro switch 12 is interposed in the conductor W3 and prevents operation of the solenoid I90 in response to closing of the switch '2I5, 251 until the heater 06 has reached the lower limit of its travel.

A stop gun gang switch lever, which is shown on the panel 19 at 245 operates a normally closed switch 265 interposed in conductor I8I and a normally closed switch 261 which normally shortcircuits a high resistance element 223 of the voltage accumulator circuit I99. The lever 245. in one position closes the switches 265 and 201 for normal operation of the machine. When the lever 245 is thrown to its other position, switches 265 and 261 are opened, having the effect of preventing movement of the dirnpling gun assembly 20 and increasing the time interval required to charge the grid 20I sufficiently for passage of current from anode I to cathode I 82 of the gas trigger tube I34.

The machine is also designed for dimpling dural orother metals which may be worked cold without the development of structural weakness. A thumb knob mounted on the panel" 19, and indicated in Figure 2 by the numeral 92, operates four switches which appear on the wiring diagram of Figure 3 and are designated by the numerals 269, I98, 21I and 212. Switch 269 is interposed in conductor I5! and when open prevents energization of the relay coil I 49 which controls the heater circuit. Switch I98 has two positions, designated on the diagram as M and D. When this switch is in position M conductor I81 is connected to conductor I61 permitting operation of the pressure valve I 06 and discharge valve II2. When it is in position D it shortcircuits the voltage accumulator discharge circuit I99, connecting this circuit through conductor 229 to conductor I61.

Switch 21I has two positions, indicated by the letters M and D. When in the position M conductors HI and I13 are connected completing the circuit for operation of the valve I06. When in position D conductor I83 is connected to conductor I13 through a cross-circuit conductor 225 for energization of solenoid I 99 for the operation of pressure valve I94 lowering the dimpling gun assembly.

Switch 212 has two positions, designated by the letters M and D. When this switch is in position M conductor I11 is connected to con ductor I19, completing the circuit to solenoid I96 for the operation of discharge valve H2 to retract the heating elements to their normal positions. When this switch is in position D it connects conductor I89 with conductor I19 through the cross circuit conductor 221, completing a circuit for the operation of solenoid I92, which actuates discharge valve IIO for the elevation of the dimpling gun assembly.

When the thumb knob 92 is turned to the lefthand position, as shown in Figure 2 and designated Dow, switch 269 is closed and switches I98, 2H, and 212 are in their M position. When the knob 92 is in the right-hand position, designated Dural, switch 269 is open and the other three switches are in their D position,

The heating elements 52 and 60 and the dimpling dies 59 and 10, are shown in Figures 5 and 6. The heating element 52, as above described, is circularly apertured for encirclement of the upper die 59, and consists of a shell 204, a layer 206 of heat insulating material, heating conductors 249 in an electrical insulating sheath 25L and a facing 2M of preferably pure silver or of copper with a heavy plating of pure silver on its lower heating face. The lower heating element 56 similarly comprises a shell 2I6 secured to the upper end of the piston 64, a layer ofheatv insulation 2I8, heating conductor 253 in an insulating sheathing 255 and a facing 220 of pure silver or of copper with a heavy plating of pure silver on its heating face. The silver has the combination of high specific heat, high conductivity and non-oxidizing qualities, which make it one of the few materials, if not the only material, which is practical as a contact facing.

The piston 64, as has been above described, is tubular and slides vertically upon a tool support 251 which carries the lower male die 10. When a magnesium sheet 208 is placed in the machine for the dimpling operation, one of the previously drilled rivet holes therein is placed upon a pilot 222 of the die 10, the sheet being supported by the conical connection 26I between the pilot 222 and the body of the die 10.

The heating elements are designed to have different temperatures, the lower heating element 66 being maintained for example at a temperature preferably of about 650 and the upper heater being maintained at a temperature of preferably 900 for dimpling the hard rolled magnesium alloy known as Dow metal J, the composition of which is 92.5% magnesium, 6.5% aluminum, and a remainderof zinc and manganese. The lower heating element in its normal retracted position is spaced relatively close tothe sheet of magnesium metal and the upper heater 52 is spaced relatively distant therefrom. The heating face of the lower element 66 is also preferably greater in area thanthe heating face of the upper heating element 52. The capacity of each heater is sufficient to maintain its heating surface at its prescribed temperature.

As a result of these relative heating capacities, heating surface areas, and spacings from the metal sheet, the two heating elements, while held in their retracted position, will, by radiation and to some extent by convection of air currents, heat the metal sheet, although to a degree substantially'less than 650, the upper heating element contributing to a substantially.

lesser extent to this heating action.

As the heating elements are moved into and out of contact with the sheet to successively dimple a row of rivet holes, the temperature of the area surrounding any given rivet hole will rise as the operator moves it toward the dimpling dies, reaching a temperature of 650, or nearly that temperature, when it is between the dimpling dies.

When at this juncture the heating elements are moved into contact with the metal sheet, the upper heating element acts to bring the temperature of the metal sheet rapidly to the optimum working temperature of approximately 650 in a relatively few seconds. In the operation of the machine, after a metal sheet is initially heated prior to the first dimpling operation thereon, it

requires as little as two seconds of contact of the heating elements with the sheet for bringing that portion of it surrounding a rivet hole to proper working temperature. The upper heater will not overheat the metal in this brief time interval, since the lower heater, being at 650 and of larger size and having a silver facing, will'absorb heat from the upper heater and inhibit a rise in the temperature of the metal sheet.

After the temperature of the heating elements has been regulated to those values suitable for heating a given material to forming temperature, the variable resistor H6 is adjusted to provide a time interval of contact of the heating elements with the sheet which will give the sheet optimum temperature for the desired forming operation.

It is important that the sheet be brought accurately to this temperature. If, for instance, the operation is that of dimpling and the adjustment provides too high a temperature, the dimples will be indented too deeply and the sheet will warp. If the temperature is too low, the sheet will develop cracks around the dimple.

A thermocouple (not shown) is embedded in the silver facing of each heating element. Referring to the wiring diagram of Figure 3, the thermocouple of the upper heating element is connected by conductors IBI and I63 to the terminals on one side of a double-throw switch 86. The thermocouple of the lower heater is connected by conductors I 51 and I59 to the terminals on the other side of this switch. The movable arms of this switch are connected by conductors 214 and 215 to an electric temperature meter 84. The movable arms of the switch 86 are held by a spring normally in engagement with the terminals of the conductors I51 and I59, since it is more important that the operator have indicated the temperature of the lower heater. This is true because, as has been explainedabove, this heater is normally maintained at a temperature less than the upper heater and as it absorbs heat from the sheet the temperature thereof will more closely approximate the temperature of the sheet. When the operator desires to check the temperature of the upper heater he may do so by'throwing the switch 86 to connect conductors IGI and I63 with conductors 214 and 275 leading to the meter.

In Figure 3, there is shown a conductor 233 leading off from conductor I56 between the variable tap of the transformer I58 and switch I56. This may be connected as shown in Figure 4 to one of the heaters, preferably the lower heater, this connection and the conductor I60 connecting the transformer coils, establishing a circuit for the lower heater which bypasses the transformer coils, so that manipulation of the transformer l58'by the operator will regulate the temperature of one heater only, which prefera'bly is the upper heater.

The heating elements 52 and 66 are so constructed and secured in place that they are readily removable, the flexible cable leading thereto being provided, as shown in Figure 1, for that purpose with jacks at 226 and 228, This feature of construction of the machine is of advantage in that it makes it possible to change the heating elements using for metal sheets of different thickness and of different curvature, heating elements of corresponding character.

As shown in Figures '7 and 8, the heating face of the upper heating element is formed with slots 230 for clearing previously formed dimples after the metal sheet is moved laterally of the heating elements.

In Figure 9, the contact face 218 of a heating element 52' is substantially smaller in area than the heating chamber 279 whereby heat may be applied to the metal sheet in a concentrated manner;

The panel 79 at the end of the control box I8, as shown in Figure 2, mounts the. switch 86 for selectively connecting the thermocouples of the heaters with the temperature meter 84, which Dow position and the line switch 83 is closed. Closing of the line switch 83 lights the beacon lamp 82, energizes the heating circuitrelay I 49, closing switch I58 to pass current through the heaters 52 and 66. The temperature of the heaters is regulated by adjustment of the transformer I88, accomplished by manipulating the transformer manipulating knob 88. Since the two heaters are connected in parallel, the temperature of the heaters are proportionately raised or lowered together. However, if the heaters are connected, as shown in Figure 4, the temperature of the one heater may be regulated without affecting the temperature of the other heater.

A sheet of magnesium alloy is now placed in the machine with one of the rivet holes therein placed upon the pilot 222 of the lower die 18, radiation from the lower heating element, and to a lesser extent from the upper heating element, causing a substantial elevation of the temperature of the metal sheet. Closing of the line switch 83 also sends current through'filament I14 of the rectifier tube 118. If, as is usually the case, it is desired to preheat the metal before dimpling the first rivet hole in the sheet, stop gun gang switch 245 is temporarily thrown at this time, opening switches 265 and 281.

Upon depression of they foot lever 98, current flows to the control relay I86 which connects the circuit leading to the pressure valve I88 and opens the switch in conductor 283. Current now flows through conductor I69 to the solenoid I 94, actuating pressure valve I88 operating the piston in cylinder 48 and the piston in cylinder 68 to bring the heating elements in contact with the metal sheet. While the heating elements are held against the metal sheet by va1veI88, voltage is being built up in voltage accumulator circuit 288,

and at the end of a time interval, which may be regulated for example at two seconds by adjustment of the knob 98, the gas trigger tube I84 is conditioned for passage of direct current from the rectifier tube I18 through the direct current control relay coil I88. When this coil I88 is ener-' gized switch 22I is opened de-energizing coil I88, switch arm '2I1 engages contact 2I5 connecting conductors I85 and I81, and disconnecting conductors HM and I81. De energization of relay coil I85 connects conductors I19'and 115 to energize solenoid I98, actuating discharge valve II2 to withdraw the heating elements to their retracted position.

De-energization of coil I88 also closes switch 2i3, permitting discharge of the RC circuit 288 through the resistance 285 resetting this circuit for the next energization of relay coil I88. The gas trig r tube I84, as is evident from the above, allow energization of relay coil I86 to hold the heating elements in contact with the metal sheet for a prescribed time interval which is unafiected reactively by the movements of the pneumatically energized devices or the flow of current through the solenoids which operate these valves. This electronic control of the heating time interval has a definite advantage over a mechanical, pneumatic or other type of time control. It is highly accurate and is unaffected by the vibration or jars which unavoidably attend the operation of the machine.

When the lower heating element closes the microswitch I2, and assuming that. the stop gun gang switch lever 245 hasv been opened, the circuit which energizes solenoid I 98, is completed except for the switch 285 which is held open by the gang switch. Since this gang switch also ISI lower the dimpling gun assembly 28.

When the sheet is brought close to dimpling temperature, the lever 245 is moved to close switches 265 and 281., shortening the time interval of contact of the heating elements with the metal sheet and closing the circuit to the dimpling gun solenoids I98 and I92. When the con trol relay coil I88 is energized by operation of the gas trigger tube I84, the lower heating element 88 will depress the button 14 closing the microswitch 12 completing the circuit to solenoid I98 for the actuation of pressure valve I84 to lower the dimpling gun assembly. When the dimpling gun assembly comes into contact with the metal sheet, if it is of the one-shot type, it will deliver its percussion blow to the upper dimpling die upon development of the prescribed pressure against the metal sheet and it is of the rattle type it will deliver a succession of blows in the manner characteristic of precussion tools of this kind.

The operator now lifts his foot from the foot lever'98, opening switch 96 which breaks the circuit to-relay I88. De-energization of relay I88 closes the circuit to solenoid I 92 which then actuates the relief valve I I8 causing the spring 42 to elevate the dimpling gun assembly to its retracted position. De-energization of relay I88 also, as described above, closes switch 221 which resets the circuit to relay I86 for its energization, when the operator shall again close foot pedal switch 98. In using the machine the operator releases the foot pressure on the pedal 98 to raise the dimpling gun at the completion of each dimpling operation and again depresses pedal 98 after he has moved the metal sheet to bring the next rivet hole into position for the next dimpling operation, whereupon the cycle is repeated.

When the machine is used for dimpling sheets of dural metal, which do not have to be heated, the knob 92 is turned to its right-hand position, opening switch 269 and placing switches I98 and 21! and 212 in their D positions. Opening of the switch 269 de-energizes relay 149, opening the switch I58 and disconnecting the heaters. Movement of the switch I98 to the D position short-circuits the voltage accumulator circuit 288 preventing charging of the grid 28I of the gas trigger tube I84, thus rendering inoperative the control relay coil I88. When the foot pedal switch 96 is now closed, current flows through the relay coil I86 connecting the switch am 289 with contact 281 and when the foot pedal switch 98 is raised the relay coil I88 is de-energized bringing the switch arm 289 into engagement with the contact 21 I. When the switch arm 289 engages contact 281 a circuit is completed through conductor I8I, solenoid I98, conductor I83 including micro switch 12 (now held closed by the heater B8) conductor 225, switch 21I, conductor I13 and conductor I15, actuating valve I84 to De-energization of the relay I86 causes switch arm 289 to engage contact 2 which completes a circuit comprising conductors I8I, solenoid I92, conductor I89, conductor 221, switch 212, conductor I ture may result in incompletely formed dimples.

This relationship of pressure and temperature may have the following theoretical explanation:

Certain metals and particularly alloys in which magnesium is the matrix and aluminum is the principal alloyed metal. have several physical states, characterized by different molecular relationships, which have a controlling influence on their forming performance. For instance, as taken from the graph shown in Figure 10 of the drawings in which ordinates are degrees of temperature and abscissae are percentages of aluminum in an alloy of magnesium and aluminum, in which A represents the liquidus line, B the solidus line and C the critical slippage line, a magnesium alloy of 5% aluminum cannot be formed without molecular changes of a weakening character at any temperature below point 0 on the critical slippage line. Between points 0 and b, it can be formed at relatively heavy pressures. For, when between these temperatures b and c, the metal is in the solidus state, and while yet crystalline, its crystalline structure will yield without fracture along both pyramidal and basal planes.

Between points a and b the metal is partly solidus and partly liquidus and the forming pressures required are lighter. At temperatures above point a, the alloy is wholly without crystalline structure and may be formed with very light pressures. If the temperature is much above point a, the mechanical properties of the alloy may be undesirably affected and there is another disadvantage in that even the lightest pressures well then thin the metal or cause it to flow. These high temperatures should therefore not ordinarily be used.

By flow is meant that internal relative movement of' component bodies of the material which is a familiar distinguishing characteristic quality of liquids. If a component body in the forming operation maintains its same proximate relation to surrounding bodies, merely changing its shape and orientation, as by means of slip plane movement, such a movement is not flow. If a component body moves into new relationships with new surrounding bodies, the material is said to flow as the word is herein'used. In flexural forming if the conditions are such, as for instance a combination of excessive temperatur and stresses, as to cause localized projections, such as wrinkles, at the edges of the forming faces of the dies, the movement of the material to form these projections is a flow movement.

Since many fiexural forming operations, such as sheet dimpling, are localized on the sheet; the heating of the sheet preparatory to the forming operation is for practical reasons also localized in character. It has been found in the case of certain materials such as Dow metal J, above referred to, that with localized heating to temperatures above point a, warping of the sheet, especially of a large thin sheet, occurs, rendering thefinished article unusable for some purposes,

as in airfoil surfaces. To overcome this warping, it has been found that by heating the sheet to a temperature somewhere between a and c, and by using a heavier forming pressure, warping is eliminated and perfect forming is at the same time secured. The pressure must not, however, be suflicient to appreciably flatten the sheet or cause it to appreciably flow. Insufficient pressure, depending on the temperature, will result in an incompletely formed product. In any event the temperature of the sheet must not be below point c On the critical slippage line or fracture will result. The critical slippage point is that temperature below which these metals will not yield under pressure along both Pyramidal and basal planes without fracture.

Forming the metal sheet at a lower temperature and at a correspondingly higher pressure has an additional advantage for certain job requirements. Higher forming pressures of a percussive character have a work hardening effect on the metal. Where this'work hardening is an advantage in the finished product, it may be accomplished with metals, such as the magnesium alloys herein described, by adjusting the percussive pressure of the dimpling gun or other forming tool to a value which is sufficient to work harden the formed zone and heating the metal to a corresponding temperature between points a and 0.

While the Value of the fluid pressure causing movement of the heating elements into contact with the metal sheet may vary substantially without disadvantage, it should not be so great as to injure the metal sheet nor so small that the heating faces of the elements will not contact the metal sheet with sufiicient firmness to provide free conduction of heat from the heating element to the'metal.

It will beunderstood that, if desired, the temperature of the heating elements can be thermostatically controlled by the addition of suitable automatic regulatory devices for this purpose, such as are well-known in the electric heating art.

While there have been described herein certain embodiments of this invention, the invention is not to be understood as confined to these particular embodiments, but is to be given the definition and scope expressed in the following claims.

If desired, the machine may be adjusted to hold the heating elements stationary in their retracted position and the heat within the dies which is received from the encircling heating elements relied upon to raise the metal sheet to proper forming temperature at the time the dies contact the sheet when brought into forming position. To successfully carry out this method the heating elements must be maintained at a higher temperature for any given forming pressure than their temperature when used in the contact method above described and also the dies must be made of a material which will not lose hardness or other qualities desirable in die forming work, at the temperature required to thus bring the metal sheet to forming temperature. Preferably the material of the die should be relatively non-oxidizable at such a temperature and of high specific heat; and high thermal conductivity.

The expression heating element or body as used herein is not to be limited to an electrically heated element or body, except where modifying or amplifying context implies such a limitation. The expression defines a body or member which has or is associated with heat delivering means whereby its temperature may be heating raised, whether that means he an electric current conductor, a heated fluid like steam, or other means.

Specific temperature values mentioned herein are uniformly on the Fahrenheit scale.

We claim:

1. In a machine for forming plates and other objects of metals and other materials at relatively high and critical forming temperatures, including means for forming the plates and other objects while at said temperatures, the combination of: means for holding the plate; a first heating body independent of the forming element of the machine and arranged on one side of the held plate; a second body independent of the forming element of the machine and arranged on the opposite side of the held plate; means for maintaining the first body at a substantially constant normal temperature of a first degree which is not greater than the desired formingtemperature of the work article; means for maintaining the second body at a substantially constant normal temperature of a second and substantially greater degree which is greater than the desired forming temperature of the work article; means for initially relatively disposing the heating bodies and plate for radiantly heating the plate by said heating bodies; and means for thereafter relatively disposing the heating bodies and plate for conductively heating the plate by said heating bodies preparatory to the forming operation.

2. In a machine for forming plates'and other objects of metals and other materials at relatively high and critical forming temperatures, including means for forming the plates and other objects While at said temperatures, the combination of: means for holding the plate; a first heating body independent of the forming element of the machine and arranged on one side of theheld plate and normally held in spaced relation therewith; a second heating body independent of the forming element of the machine and arranged on the opposite side of the held plate and normally held in spaced relation therewith; means for maintaining the first body at a substantially constant normal temperature of a first degree which is not greater than the desired forming temperature of the Work article; means for maintaining the second body at a substantially constant normaltemperature of a second degree substantially greater than said first degree which is greater than the desired forming temperature of the work article; and means for sequentially, first simultaneously moving said heating bodies into contact with the two sides of the plate respectively, then after a brieftime interval retracting said heating bodies to their normal position preparatory to the forming operation,

3. The combination defined in claim 2,, and in addition thereto; means for adjusting the normal temperature of one ofsaid heating bodies independently of the normal temperature of the other heating body.

4. The combination defined in claim 2, in which said heating bodies are electrically heated and connected to a current source in parallel, and in addition thereto; means for adjusting the wattage input to said heaters.

5. The combination defined in claim 2 in which said first heating body is normally positioned rel atively close to said metal plate for heating said plate to a temperature approximating but substantially less than that of said first heating body when in said normal position and said second heating body is normally positioned relatively distant from said metal plate and sufliciently spaced therefrom to prevent heating of said plate to a temperature in excess of that of said first heating body.

6. The combination defined in claim 2 in which said first heating body is of relatively large capacity and the area of the heating surface thereof juxtaposed to said metal plate is relatively large and said second heating body is of relatively small capacity and the area of the heating surface thereof juxtaposed to said metal plate is relatively small.

'7. The combination defined in claim 2 and in addition thereto, means for regulating said first heating body whereby its constant normal temperature is approximately the optimum forming temperature of the metal of said plate, said first and second heating bodies being of respective heating capacities, sizes of heating faces and normal spaced disposition with reference to said plate such as to inherently heat the plate, when said first heating body is at said optimum forming temperature and said second heating body .is at a substantially greater temperature and thereof to be formed and for conductive heating of said portion prior to the forming operation thereupon, said heating body including a contact facing of substantially pure silver and having a mass sufficient to give it a thermal capacity many times greater than that of the contacted portion of the work article.

9. In a machine for forming plates and other articles of metals and other materials-at relatively high and critical forming temperatures, including means for forming the plates and other objects while at said temperatures, the combination of means for holding the plate; and a heated body of extended surface area and independent of the forming element of the machine for fiat contact with said held plate at a portion thereof to be formed and for conductive heating of said portion prior to the forming operation thereupon, said heating body including a contact member of copper plated with substantially pure silver on the contact face thereof and having a mass suificient to give it a thermal capacity many times greater than that of the contacted portion of the work article.

10. In a machine for forming plates and other articles of metals and other materials at relatively high temperatures, the combination of means.

sides of said plate for forming engagement with said plate and relatively reciprocably movable along a line toward and away from said plate and coaxial with said apertures the areas of said engagement being centerd on the axis of said apertures; and means for sequentially, first simultaneously moving said bodies into contact with the two sides of said plate respectively, then after a brief time interval retracting said heating bodies to their normal positions and immediately thereafter moving said forming elements into and out of operative forming engagement with the plate each forming element being movable relative to its corresponding heater within the aperture thereof.

11. The combination defined in claim 10, in which said forming elements produce in succession a plurality of areas displaced from the plane of the plates, and the spacing of the formed areas is such as to position an earlier formed area opposite at least one of the heating bodies while the next formed area is being formed, and in which at least one of said heating bodies is grooved on its contact face to receive said earlier formed area as the plate is moved laterally between said heating bodies into position for forming the next formed area.

12. The combination defined in claim in which said forming elements are a lower male stationary dimpling die and an upper female vertically reciprocating dimpling die for use with a plate apertured for the reception of the shanks of fasteners and said plate holding means comprises the male die as a centering and levelling supporting means.

13. In a machine for forming plates and other articles of metals and other materials at relatively high and critical forming temperatures, including means for forming the plates-and other objects while at said temperatures, the combination of: means for holding the plates; 3, first heating body of extended surface area for fiat contact with the face of said plate and conductive heating thereof, said heating body including a contact member of high specific heat and high thermal conductivity; a second heating body of extended surface area for contact with the other face of said plate and for conductive heating thereof, said heating body including a contact member of high specific heat and high thermal conductivity, said heating bodies being normally disposed out of contact with and spaced from said plate, one

of said heating bodies being normally disposed nearer the plate and by reason thereof and by reason of its properties having a greater heating effect on the plate than the other heating body;

an electric temperature meter; and a switch for resiliently held in position to connect said one heating body to said meter.

14. In a machine for forming plates or other articles of metals or other materials at relatively high and critical forming temperatures, the combination of: a pair of dies for simultaneously engaging from opposite sides and forming a plate held between them; a pair of heaters on opposite sides of and normally spaced from the plate in a retracted radiantly heating position, said heaters being arranged adjacent the axis of said dies; 8. first fiuid pressure operated means for moving said heaters from said retracted position into contactual heating position with relation to the plate; means for moving said heaters from said heating position to said retracted position; means including a second fluid pressure operated means for relatively moving said dies from a retracted relative position into forming position; an automatic means for effecting in sequence in the order named the cycle of operative steps of, first actuating said first pressure operated means to move said heaters from retracted to contactual position, second after a prescribed time interval rendering said first pressure operated means in operation whereby said moving means returns said heaters to retracted position, third actuating said second pressure operated means at the completion of the contactual heating of the plate t relatively move said dies from retracted position into forming position; means for rendering said second pressure operated means inoperative; and means for relatively moving said dies from forming to retracted position.

15. The combination defined in claim 14 and in addition thereto; a non-interference means for preventing initiation of said third operative step before completion of said second operative step.

16. The combination defined in claim 14 in which the operative cycle of said automatic means is manually initiated and said means for actuating said second pressure operated means to relatively retract said dies is manually operated.

17. The combination defined in claim 14 in which said first and second fiuid pressure operated means are controlled by first and second electric circuit means respectively; and in addition thereto, a third electric circuit means for heating said heaters; and a manual gang switch for opening said first and third circuit means.

18. The combination defined in claim 14 in which said second fluid pressure operated means is controlled by a first electric circuit means and said time interval is controlled by a condenser charging second electric circuit means having a normally closed resistance cutout shunt circuit; and in addition thereto, a gang switch for opening both said electric circuit means.

19. In a machine for forming plates of metal at relatively high and critical forming temperatures, a combination of: a pair of dies for simultaneously engaging from opposite sides and forming a plate held between them; a pair of heaters on opposite sides of the plate; resilient meansfor normally holding said plates in a retracted position, said heaters being arranged adjacent the axis of said dies; a first fiuid pressure operated means for moving said heaters from said retracted normal position into heating position with relation to the plate; a first valve means having a first and second position for operating said first fluid pressure operated means, said first position efiecting movement of said first pressure operated means to move said heaters into heating position, said resilient means returning said heaters to said retracted position when said valve means is in said second position; a second fluid pressure operated means for relatively moving said dies from a relatively retracted position into a forming position; a second valve means having a first and second position for operating said second pressure operated means the first position of saidsec 0nd valve means causing said second pressure operated means to move said dies into forming position; means for returning said dies to said retractive position when said second valve means is in said second position; a first solenoid for moving said first valve means to said first position; a second solenoid for moving said first valve means to said second position; a third solenoid for moving said second valve means to said first tric power circuit; a master switch for said eleca control shunt circuit; a manual switch in said control shunt circuit; 'a first control relay in said control shunt circuit; a first-shunt-circuit connected t said first solenoid; a normally open first-shunt-circuit switch; a second-shunt-circuit connected to said second solenoid; a normally closed second-shunt-circuit switch; a thirdshunt-circuit connected to said third solenoid; a first, normally closed, third-shunt-circuit switch; a second, normally open, third-shunt-circuit switch; a fourth shunt circuit connected to said fourth solenoid; a normally closed, fourth-shuntcircuit switch; a rectifier tube having a filament connected across said electric power circuit and an anode and a cathode connected in parallel with said control relay; a gas trigger electronic tube having a grid, an anode and a cathode; a voltage accumulator circuit between said rectifier cathode and said gas trigger tube grid; a second control relay "circuit connected between said rectifier cathode and said gas trigger tube anode, said gas trigger tube cathode being connected to place said second control relay in parallel with said first control relay; a voltage discharge circuit for discharging said voltage accumulator circuit; a normally closed switch in said discharge circuit; a normally closed switch in said first control relay circuit, said first control relay when energized closing said first-shunt-circuit switch, opening said secc-nd-shunt-circuit switch and opening said discharge circuit switch, and said second control relay when energized opening said first control relay circuit switch, closing said second thirdshunt-circuit switch and opening said fourthshunt-circuit switch, and one of said heaters opening said first third-shunt-circuit switch when moved from retracted position.

.20. The combination defined in claim 19 and in addition thereto; a resistance shunt circuit for said voltage accumulator circuit; a normally closed switch in said voltage accumulator circuit in parallel with said resistance shunt circuit; a normally closed switch means for opening said first and second shunt circuit means; and a manual gang control for opening said last mentioned switch and switch means.

21. The combination defined in claim 19 and in addition thereto; a potentiometer connected in said voltage accumulator circuit for adjusting the time rate of voltage increase in said circuit.

22. The combination defined in claim 19 and in addition thereto; a normally open switch means for closing said heater shunt circuit, a relay for closing said switch means and a relay circuit for energizing said relay, connected across said power circuit; a first selective switch for closing said relay circuit in a first position and opening said re lay circuit in a second position; a second selective switch in said third shunt circuit for either closing said third shunt circuit in a first position or for short-circuiting said voltage accumulator circuit in a second position; a third selective switch for connecting said first shunt circuit switch to saidfirst solenoid in a first position or to said third solenoid in a second position; a fourth selective switch for connecting said second shunt circuit switch to said second solenoid in a first position or to said fourth solenoid in a second position; and a manual gang selective means for placing all of said four selective switches either in their first positions or in their second positions.

23. In a machine for localized forming of plates and other objects of metals and other materials at relatively high and critical forming temperatures, including means for forming the plates and other objects while at said temperatures, the combination of means for holding the plate; a first heating body independent of said forming means and arranged on one side of the held plate, said heating body having a heating surface facing toward and conforming to the juxtaposed local plate portion to be'formed and normally held with said heatingsurface in spaced relation with said plate portion in position to radiantly heat said plate portion; a second heating body independent of said forming means and arranged on the other side of the held plate, said second'body having a heating surface facing toward and conforming to the juxtaposed local plate portion to be formed and normally held with said heating surface in spaced relation with said plate portion in position to radiantly heat said plate portion; and automatic means for sequentially, first simultaneously moving said heating bodies into contact with the two sides of said plate respectively, then after a brief predetermined interval retracting said heating bodies to their normal position preparatory to the operation of said forming means.

24. The combination defined in claim 14, and

in addition thereto: manual means for rendering inoperative said second fluid pressure operated means and lengthening said time interval.

25, In a machine for forming plates and other objects of metals and other like materials, at

relatively high and critical forming temperatures, the combination of means for holding the plate; a movable body having means for heating the body and normally held in spaced relation with the plate for radiant heating thereof; a forming means movable into and out of forming engagement with the plate; means for moving said body into and out of contact with the plate for heating the plate by thermal conduction, said heating means being effective on said body in either spaced or contact position thereof; and

' means including means made operative by movement of the body out of engagement for subsequently moving said forming means into. forming engagement with the plate.

26.,In a machine for a localized forming of plates of metals or other materials at relatively high or critical forming temperaturesthe combination of: means for holding the plate; a body; means for heating the body; means for moving the body into and out of engagement with the plate at the locus desired to be formed; said body locally heating the plate by thermal conduction when in engagement therewith; means additional -to and separate from said body for forming the plate while the plate at said locus is at a temperature caused by said conductive heating, and means for moving said forming means into forming engagement with said heated locus, said means including means made operative by the movement of said body out of engagement with said plate so that said forming means is moved into forming engagement with the locus while the temperature of the same is at the critical forming temperature.

27. A machine for forming plates and other like objects of metals and other material comprising means for heating a plate; a heating element slidably mounted for movement into and out of engagement with said plate; means for normally holding said element out of engagement with said plate; means for moving said element into engagement with said plate to heat an area thereof; forming means movable int and out 01 forming engagement with the heated area of said plate; means for rendering said moving means operative to move said element into engagement with said plate against the action of said holding means; means for timing said engagement whereby said moving means is rendered inoperative after a predetermined lapse of time, whereby said holding means returns and holds said element out 10 of engagement with said plate; means for moving said iorming means into forming engagement with said plate; and means including means actuated by movement of said element out of engagement with said sheet for rendering the means operative for moving said forming means into forming engagement with the heated area of the plate.

GEORGE D. RECHTON. DELBERT J. WARD. JACK H. WATSON. 

